The BJCMGT is excellent. I had a buggy board on the back of the BJCM this week and I suspect its much easier on the GT because of the adjustable handle and larger handle space. Have a look also at the Baby Jogger City Versa which is at the top end of your budget with GT wheels on, but it gives you a small, one handed, easy folding package which also parent faces. Plus again a buggy board should fit on the back, but dont quote me on that! The Easywalker June is my other recommendation of 2012 because these two pushchairs really are as near perfection as you can get!! But it will be over budget with the carrycot although I am sure the seat is suitable from birth without one. Again I am sure Easywalker will have a board that fits.
Just as a more off the wall suggestion, when our eldest used to tire we used to push our baby right up to the back of the BJCM recline strapped in and the older one had tons of room to perch sat squarely on the seat pad with an additional harness on the D rings. Unconventional but it worked great for odd outings and for me is preferable to a buggy board. But it wouldn't work with a carrycot.

It didn't affect stability on my BJCM4 although when DD decided to lean back it was starting to feel tippy and I was glad of the 4 wheels instead of 3! I didnt kick the board simply because I walked to the side. I push one handed anyway so I put the board at the other side. I can't say I like buggy boards though. I much prefer a double. I would think the GT would be better because of the space between the pushchair and the handle. I haven't had chance to dig my Elite out to try the Bumprider on as yet but the Elite is quite back heavy too so I dont know how we would get on.
Re stockists - try Winstanleys Pramworld, Ladybugs and Itsababy. I believe Kiddicare are getting the BJCM in too and that they have some other Baby Joggers online.

Hi, I have the baby jogger gt and the glider board and it works well for us. It definitely works better with the adjustable handle (I have the bjcm4 and it doesn't work well with the fixed handle) but the gt and elite are great with it. I have never had any issues with it being unstable. As you have a long stride this may be an issue for you as I would say you may clip the board but I do feel this would be an issue with most buggyboards and prams. As tiggywunkle says the baby joggers are easy to push one handed so you would manage to find a way to push it that suits you.
It's a shame you can't test it out beforehand.
One thing I have to note is that when the glider board is attached the pushchair doesn't fold well so either needs to be removed or have the space (in the boot for example) to put the half folded pushchair.
If you have any other questions I would be happy to answer them for you.
Keep meaning to take some photos and write a wee review for best buggy so others can see what it is like!
Now I have to decide what one to keep - the bjcm4, bjcmgt or the bjelite - or ... Someone can help me by backing up my claim to hubby that they are all different and are all necessary in my everyday life so I have to keep them all!
Good luck with your search!